1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, which is applied to machine tools, industrial robots, precision machines and testing equipment and in which a slider comprising a casing and end caps is slidably mounted on a track rail through rolling elements.
2. Description of the Prior Art
The linear motion rolling guide unit generally has a slider mounted slidable on a track rail through rolling elements, the slider comprising a casing and end caps. To describe in more detail, the linear motion rolling guide unit comprises: a track rail having raceway grooves formed on both longitudinal sidewall surfaces thereof; a casing mounted slidable on the track rail and having raceway grooves formed therein that face the raceway grooves of the track rail; end caps attached to the longitudinal ends of the casing; rolling elements rolling between the opposing raceway grooves; end seals attached to the outer end surfaces of the end caps; under seals provided to the underside of the casing on both sides; and a top seal provided to the underside of the casing which faces the top surface of the track rail.
In the linear motion rolling guide unit, foreign matters such as dirt, dust and chips, once they adhere to the raceway grooves of the track rail and slider, block the smooth running of the rolling elements as the slider slides on the track rail, and will eventually damage the raceway grooves shortening the life of the product. To prevent this, the linear motion rolling guide unit has end seals, under seal and top seal as sealing means between the slider and the track rail.
Of the sealing means, the end seals effectively remove foreign matters adhering to the top surface of the track rail. When foreign substances collect in bolt holes in the track rail, it is difficult to remove them completely by the end seals. Foreign matters that have moved past the end seals are scattered inside the slider and may enter into the raceway grooves where the rolling elements are running. To prevent the foreign matters that have passed the end seals unhindered from entering into the raceway grooves, a top seal is provided.
The raceway grooves of the track rail and the slider are supplied with grease. When grease adheres to the upper surface of the track rail, foreign matter sticks to the upper surface of the track rail and becomes difficult to remove by the end seals alone. The linear motion rolling guide unit has the top seal to prevent grease in the raceway grooves from leaking onto the top surface of the track rail.
The top seal has two functions of preventing foreign matters from entering the raceway grooves and of preventing grease from leaking into the top surface of the track rail.
As disclosed, for instance, in Japan Patent Utility Model Publication No. 35945/1987, the conventional top seal consists of a flat elongate plate and a longitudinally extending single rubber lip secured to the edge of the plate. The lip is inclined outwardly toward the raceway grooves of the casing, with the end of the lip pressed against the top surface of the track rail by its own elastic force. It is noted that the top seal has only one lip for sealing.
Another example of the top seal, disclosed in Japan Utility Model Publication No. 2026/1994, consists of a leaf spring made of a bent steel plate with its convex bent portion face up to make it elastic, and a pair of seal plates fixed to the edges of the leaf spring and extending longitudinally of the track rail. The seal plate is almost rectangular in lateral cross section and has two or more projected strips extending longitudinally on its underside. The underside of the seal plate is pressed against the upper surface of the track rail by the leaf spring to make longitudinal line contact with the upper surface of the track rail. Because the top seal has its seal plates pressed against the upper surface of the track rail by the elastic force of the leaf spring, the sealing performance of the top seal depends on the machining precision of the leaf spring. Therefore, when the machining precision of the leaf spring is bad, a sufficient pressing force to press the seal plates against the upper surface of the track rail is not produced, resulting in ingress of foreign matters and leakage of grease. Further, because the spring plate of the top seal is made by bending the steel plate in a convex shape, it is necessary to secure a gap between the underside of the slider and the upper surface of the track rail, making it difficult to reduce the size and thickness of the unit.
Still another example of the top seal, disclosed in Japan Utility Model Laid-Open No. 82330/1989, is a seal plate which extends longitudinally of the track rail and has an almost rectangular lateral cross section. The top seal is secured directly to the underside of the slider that opposes the upper surface of the track rail so that the underside of the top seal does not contact the upper surface of the track rail with a small gap therebetween. The top seal, because it does not contact the track rail, functions as a labyrinth seal but cannot perfectly block the leakage of the grease.
A further example of the conventional top seal is shown in FIG. 6 and 7. The top seal 60 comprises a plate 65 mounted to the inner underside 62 of the slider 61, U-shaped in lateral cross section, and facing the upper surface 64 of the track rail 63; and a pair of seal plates 66 secured to edges of the plate 65 and extending longitudinally of the track rail 63 (for example, Japan Patent Laid-Open No. 26236/1993).
The plate 65 is made of a flat steel plate, which has a base portion 68 whose width size is set larger than the diameter of the bolt hole 67 formed in the track rail 63, and a bent portion 69 made by bending the edges of the base portion 68 along the longitudinal direction. At the longitudinal ends of the plate 65, as shown in FIG. 7, a pair of elastic, slender insertion portions 70 are formed projectingly. By inserting the insertion portions 70 into insertion grooves formed at the side surfaces of the end caps, the top seal 60 is fixed to the slider 61.
Each of the seal plates 66 has an end lip 71 that contacts the upper surface 64 of the track rail 63 and which is inclined inwardly so that they approach each other. In other words, the end lips 71 are inclined toward the central area of the track rail 63. The elastic force of the seal plates 66 and of the insertion portions 70 of the plate 65 urges the end lips 71 of the seal plates 66 to press against the upper surface 64 of the track rail 63 with a predetermined pressure, thus forming a sealing plane.
The mounting of the top seal 60 to the slider 61 is done at the same time that the end caps (not shown) are attached to the longitudinal ends of the casing. With the insertion portions 70 of the plate 65 inserted into the insertion grooves formed in the side surfaces of the end caps, the end caps are fixed to the casing by screws, thus securing the top seal 60 to the slider 61.
The seal plates 66 have their end lips 71 pressed against the upper surface 64 of the track rail 63 by the elastic force of the insertion portions 70 of the plate 65 and also inclined inwardly toward the central area C of the track rail 63. This construction makes it difficult for foreign matters to enter into the raceway grooves 74, 75. However, because the end lips 71 are inclined inwardly toward the central area C of the track rail 63, when the pressure in the storage chamber 73 becomes high by the supplied grease, the end lips 71 of the seal plates 66 are pressed open toward the central area C of the track rail 63, letting the grease leak out into the central area C of the track rail 63. As a result, the grease that has leaked from the storage chamber 73 remains on the upper surface 64 of the track rail 63, causing foreign matters to adhere to the upper surface 64 of the track rail 63. Then, it is difficult to wipe away foreign matters sticking to the upper surface 64 by the end seals 76.
The assignee (Nippon Thompson Co., Ltd.) of this invention, therefore, developed a linear motion rolling guide unit having a top seal as shown in FIG. 3, 4 and 5 and filed the Japan Patent Application No. 101540/1994 for patent of the top seal. The linear motion rolling guide unit applied for patent comprises a track rail 31 installed on a base 31A and having raceway grooves 39 formed in longitudinally extending sidewall surfaces 41 thereof, and a slider 37 slidably mounted astride the track rail 31. Grease supplied from a grease nipple (not shown) is stored in a storage chamber 42A in the casing 32 to lubricate the raceway grooves 39 in the track rail 31 and the opposing raceway grooves 39 in the casing 32. End seals 36 has a sealing portion (not shown) that makes sliding contact with the sidewall surfaces 41 and the raceway grooves 39 of the track rail 31. The end seals 36 also have a seal projection 36A that is in sliding contact with the upper surface 44 of the track rail 31. The under seals 33 provide vertical sealing for the track rail 31, casing 32 and end caps 35. The top seal 49 is provided between the underside 43 of the casing 32 of the slider 37 and the upper surface 44 of the track rail 31. The underside 43 in a hollow portion 42 of the casing 32 of the slider 37 is formed with a recess 45 that opposes the upper surface 44 of the track rail 31. The underside 43 of the casing 32 are formed with holes 46 on the center line.
The top seal 49 has a plate 50 attached to the underside 43 of the casing 32. The plate 50 extends over the entire lengths of the underside 43 of the casing 32 and of the underside 43A of the end caps 35, and the end surfaces 50A of the plate 50 are in hermetic contact with the end seals 36. The top seal 49 also has a pair of lip seals 51, 52 secured to the edges of the plate 50. The plate 50 has bent portions 53 that are made by bending the edge portions of a flat steel plate along the longitudinal direction. The plate 50 has cylindrical projections 55 which enclose mounting holes 54. The cylindrical projections 55 are formed at positions corresponding to the holes 46 in the underside 43 of the casing 32.
The lip seals 51, 52 are made of elastic material such as rubber and plastics and are in sliding contact with the side areas S of the upper surface of the track rail 31. The lip seals 51, 52 are each secured to the plate 50 through a mounting base 56 and branch into an inner lip portion 57 and an outer lip portion 58. The inner lip portion 57 is inclined inwardly toward the central area C of the track rail 31 while the outer lip portion 58 is inclined outwardly in a direction opposite to the inner lip portion 57. The inner and outer lip portions 57, 58 are in sliding contact with the side areas S of the upper surface 44 of the track rail 31. The lip seals 51, 52 are secured to the plate 50 through burning by engaging a mounting step portion 59 of the mounting base 56 with the bent portion 53 of the plate 50.
In the top seal, the lip seals 51, 52 extend from the mounting base portions 56 and branch at their ends into two: the inner lip portion 57 inwardly inclined from a branch point 48 toward the central area C of the track rail 31 and the outer lip portion 58 outwardly inclined from the branch point 48 in a direction opposite to the inner lip portion 57. The inner lip portion 57 and the outer lip portion 58, on receiving an external force, tend to rotate together about the branch point 48. That is, when the pressure in the storage chamber 42A becomes high, the outer lip portion 58 rotates about the branch point 48 toward the center area C. At the same time the inner lip portion 57 tends to rotate toward the center area C. At this time, the end of the inner lip portion 57 tends to separate from the upper surface 44 of the track rail 31, so that its sealing performance is degraded, increasing the possibility of foreign matters entering through the inner lip portion 57. Conversely, when the inner lip portion 57 is pushed by foreign matters and rotated about the branch point 48 toward the side area S, the end of the outer lip portion 58 tends to separate from the upper surface 44 of the track rail 31, degrading the sealing performance of the outer lip portion 58 and increasing the possibility of the grease moving past the outer lip portion 58 and being discharged onto the upper surface 44 of the track rail.